Hey Sharp,
I own a few BSA Martinis I use for competition and play. Great rifles for the price. Most will shoot well if they've been upkept. Parts are alittle hard to find so I buy whatever I can find, but they are very robust in construction. I shoot a MkIII inter. rebarreled by Karl Kennon for prone. I like the very fast lock time of these guns.
As for pricing, for a MkIII inter. RH W/sights about $550 is the going rate for a 90%-95% rifle, but you'll pay as much as it's worth to you. I payed $750 for one of my MkIII inter LH w/o sight in 98% condition and have no regrets. Hope this was of help.
Shoot well, ATO